Eocene Sediments Research Articles

Calcareous nannofossil biostratigraphy of Nag El Quda, South of Dababiya, Eastern side of the Nile Valley, Egypt.

The biostratigraphy of calcareous nannofossils of the upper Paleocene-lower Eocene sequence in Nag El Quda area (South of Dababiya, Eastern Side of the Nile Valley, Egypt carried out in detail. This study of the P-E transition, allow us to recognize some of the prominent and abrupt events that characterize the P/E boundary, and to relocate this boundary with respect to the recent redefinition of the Paleocene/Eocene boundary. The present stratigraphic study of the P/E interval based on close sampling. This study has provided a high resolution litho- and biostratigraphic data based on calcareous nannofossils. The study interval includes from the base to top; El Hanadi, Dababiya, and El Mahmiya members. The P/E boundary is situated at the NP9a/NP9b boundary, which lies at El Hanadi/Dababiya contact. We identify the first occurrence (FO) of excursion taxa (Discoaster anartios, D. araneus, Rhomboaster spp.) at the base of the Eocene. These taxa are adapted to warm climatic conditions that prevailed at this boundary. An abrupt and sharp decrease in the diversity, abundance of the genus Fasciculithus occurs at the NP9a/NP9b (Paleocene/Eocene boundary), and disappeared completely shortly afterwards. The lowermost Eocene sediments studied here only yield F. tympaniformis and F. involutus.

A study of the stress state of rocks in the near-wellbore zone of the Middle Eocene sediments in the Tarsdallar deposit

A study of the stress state of rocks in the near-wellbore zone of the Middle Eocene sediments in the Tarsdallar deposit

A new species of Maomingosuchus from the Eocene of the Na Duong Basin (northern Vietnam) sheds new light on the phylogenetic relationship of tomistomine crocodylians and their dispersal from Europe to Asia

Maomingosuchus acutirostris sp. nov. is a new tomistomine crocodile from the middle–upper Eocene deposits (late Bartonian–Priabonian age, 39–35 Ma) of the Na Duong Basin in northern Vietnam. M. acutirostris can be differentiated from the type species Maomingosuchus petrolicus by having an acute anterior tip of the premaxilla. Both species differ from another Maomingosuchus from Krabi (Thailand) by differences in the surangular–dentary suture and maxillary alveoli. According to our phylogenetic results, M. acutirostris seems to be the sister species to the group M. petrolicus + Krabi-Maomingosuchus. The close relationship between those three tomistomines is supported in the present phylogenetic analysis by three synapomorphies. In our phylogenetic analysis, Maomingosuchus was retrieved in a basal position forming the sister group to Paratomistoma + Gavialosuchus + Melitosaurus + Tomistoma, including the extant Tomistoma schlegelii. This phylogeny indicates three different dispersal events of Tomistominae from Europe towards eastern Asia: 1) for the stem lineage of Maomingosuchus, no later than the late Eocene; 2) for the stem lineage of Penghusuchus pani + Toyotamaphimeia machikanensis, no later than the early–middle Miocene; and (3) for the stem lineage of T. schlegelii, during the Neogene. http://zoobank.org/urn:lsid:zoobank.org:pub:19B27C1E-0A3F-4425-AA8C-F904277DF327

The properties of reservoir rocks of fault traps in Yevlakh-Aghjabedi depression

The structures formed in Yevlakh-Aghjabedi depression, as well as the changes of lithofacies of reservoir rocks of fault traps have been studied based on the geophysical survey. The distribution and reservoir properties of Cretaceous, Eocene and Miocene sediments, which are essential objects for prospectivity of whole depression, have been researched as well. Alongside existing fields and prospective structures such as Muradkhanly and Zardab, non-anticline traps and the characteristics of their reservoir rocks have been studied in the areas identical for some features. Commercial recovery obtained from the upper eroded parts of cracked-porous reservoirs of volcanic sediments of Upper Cretaceous in Muradkhanly field and formation of the deposits of both carbonated and volcanogenic-sedimentary rocks in Zardab field allows supposing that separate structures formed in the same conditions along the whole studied territory may have high prospectivity. In the areas, where fault traps are associated with Paleogene sediments, which were formed by covering raised residues of the landscape or discordantly embed on the denuded surface of Upper Cretaceous, there are favorable conditions for formation of hydrocarbon deposits in carbonate-cracked or volcanogenic sediments of Cretaceous Age.

Impact of Late Cretaceous inversion and Cenozoic extension on salt structure growth in the Baltic sector of the North German Basin

AbstractThe Late Cretaceous to Cenozoic is known for its multiple inversion events, which affected Central Europe's intracontinental sedimentary basins. Based on a 2D seismic profile network imaging the basin fill without gaps from the base Zechstein to the seafloor, we investigate the nature and impact of these inversion events on Zechstein salt structures in the Baltic sector of the North German Basin. These insights improve the understanding of salt structure evolution in the region and are of interest for any type of subsurface usage. We link stratigraphic interpretation to previous studies and nearby wells and present key seismic depth sections and thickness maps with a new stratigraphic subdivision for the Upper Cretaceous and Cenozoic covering the eastern Glückstadt Graben and the Bays of Kiel and Mecklenburg. Time‐depth conversion is based on velocity information derived from refraction travel‐time tomography. Our results show that minor salt movement in the eastern Glückstadt Graben and in the Bay of Mecklenburg started contemporaneous with Late Cretaceous inversion in the Coniacian‐Santonian. Minor salt movement continued until the end of the Late Cretaceous. Overlying upper Paleocene and lower Eocene deposits show constant thickness without indications for salt movement suggesting a phase of tectonic quiescence from the late Paleocene to middle Eocene. In the late Eocene to Oligocene, major salt movement recommenced in the eastern Glückstadt Graben. In the Bays of Kiel and Mecklenburg, late Neogene uplift removed much of the Eocene‐Miocene succession. Preserved deposits indicate major post‐middle Eocene salt movement, which likely occurred coeval with the revived activity in the Glückstadt Graben. Cenozoic salt structure growth critically exceeded salt flow during Late Cretaceous inversion. Cenozoic salt movement could have been triggered by Alpine/Pyrenean‐controlled thin‐skinned compression, but is more likely controlled by thin‐skinned extension, possibly related to the beginning development of the European Cenozoic Rift System.

Eocene Sediments in the South China Sea, precursor deposits of the Oligocene expansion?

The stratigraphic record of Eocene in the Malaysian waters of the South China Sea is scarce; the few deep petroleum exploration wells and outcrops are located on the fringes of the SCS. Yet, despite the paucity of data we observe a variety of sediments that cover the range from fluviatile to (at least) neritic marine deposits. Whilst fluvial deposits dominate the Western Rim (Penyu, Malay basins), the Southern Rim (Sarawak) is characterized by deposits of a narrow and rapidly deepening shelf, with fluviatile, shallow marine clastics and carbonates passing seawards to outer shelf and neritic deposits. The proven record of the Eocene to-date is located in relatively small and deep sub-basins. Possibly, the Eocene underlies additional areas of the SCS, but there is to-date no sufficient well data to offer further confirmation. The presence of Eocene strata on the margins of Sundaland is associated with an early phase of extensional and/or transpressional tectonism, probably acting as precursor movements related to the onset of rifting of the crust underlying the SCS.

Creation of an observation network for assessment of the impact of the pig complex on the groundwater aquifer

Ukraine, as a party to the Association Agreement, in accordance with Directive 2000/60/EC of the European Parliament and of the Council, recognizes water as the most expensive resource on our planet, which must be protected and saved. Every country and every inhabitant of the planet must do everything possible to reduce the thoughtless use of water and stop water pollution. The priority is the identification of water users and "polluters", as well as the detection and prevention of pollution of water resources, which includes the identification of water sampling points around potential sources of pollution. The aim of the research is to determine the impact of pig farms on the qualitative and quantitative characteristics of groundwater using existing water intakes to preserve natural water resources from pollution and depletion. An important point for monitoring in this situation is the use of existing water intakes (bores and wells) without additional construction of observation bores and interference in the environment. To complete the study, it is necessary to create an observation (monitoring) network of selected points and establish the frequency of their study. The observation network should determine the level (static and dynamic) as well as the quality of groundwater, which reflects background concentrations (natural or "conditionally natural"). "Conditionally natural" concentrations may indicate an excess of pollutants, associated with anthropogenic impacts that occurred prior to the activities of a particular entity, in respect of which the study is conducted. Given the changes in the quality characteristics of water, caused by external factors, "conditionally natural" concentrations can be taken as background. The obtained information will allow, depending on the quality and quantity of groundwater (their level) to make management decisions on the management of groundwater resources. Groundwater in rural settlements near enterprises is in most cases the only source of water supply. The laboratory analysis of water samples from selected points in 2020 showed an excess of color, odor at 60 °C, turbidity, total iron in bores and wells. The detected elevations are due to the peculiarity of the geological structure (aquifer of Eocene sediments). The excess in the hydrogen index is almost 10 times from the surface water body, which can be taken as "conditionally natural" (background) with further study of the specific impact of the complex on the environment. The main indicators that may indicate direct contamination of the pig complex, such as nitrates, nitrites, ammonium nitrogen and microbiological studies, do not exceed the normalized values, set for drinking water. In this case, the specific indicators are within normal limits. Petroleum products were not detected in the studied samples

Sedimentary Provenance Changes Constrain the Eocene Initial Uplift of the Central Pamir, NW Tibetan Plateau

The Pamir Plateau region of the Northwestern Tibetan Plateau forms a prominent tectonic salient, separating the Tajik and Tarim basins. However, the topographic evolution of the Pamir Plateau remains elusive, despite the key role of this region played in the retreat of the Paratethys Ocean and in aridification across Central Asia. Therefore, the SW Tarim and Tajik basins are prime locations to decipher the geological history of the Pamir Plateau. Here, we present detrital zircon U/Pb and apatite fission-track (DAFT) ages from the Keliyang section of the SW Tarim Basin. DAFT ages show that sediments had three components during the Late Cretaceous and two components since the Oligocene. Detrital zircon U/Pb ages mainly cluster between 400 and 500 Ma during the Late Cretaceous, and coincide with ages of the Songpan-Ganzi and the West Kunlun Mountains. In contrast, detrital zircon U/Pb ages in the Eocene sediments are centered at around 200–300 Ma and 40–70 Ma, with a peak at ∼45 Ma, consistent with data from the Central Pamir and the West Kunlun Mountains. The ∼45 Ma peak in detrital zircon U/Pb ages since the Eocene indicates a new sedimentary source from the Central Pamir. Non-metric multi-dimensional scaling (MDS) analyses also show that the sedimentary source was closer to the Central Pamir after the Eocene, when compared to the Late Cretaceous. The result shows a clear Eocene provenance change in the Keliyang area. Moreover, this Eocene provenance shift has been detected in previous studies, in both the Tajik and Tarim basins, suggesting that the entire Central Pamir region likely experienced quasi-simultaneous abrupt uplift and paleo-geomorphological changes during the Eocene.

New late Eocene and Oligocene plotopterid fossils from Washington State (USA), with a revision of “Tonsala” buchanani (Aves, Plotopteridae)

AbstractWe report new specimens of the Plotopteridae from Washington State (USA), an area where these flightless seabirds underwent significant diversification during the late Eocene and Oligocene. To date, five plotopterid species from western Washington have been formally named. Specimens previously assigned to Tonsala buchanani Dyke, Wang, and Habib, 2011 belong to at least two, but probably even three, different species. One of these, the large-sized “Whiskey Creek specimen” from late Eocene deposits mapped as the Makah Formation, is the oldest known plotopterid and is here tentatively assigned to ?Klallamornis clarki Mayr and Goedert, 2016. Another specimen originally referred to T. buchanani is also likely to belong to a different species and is among the most substantial records for North American plotopterids. We formally transfer T. buchanani to the taxon Klallamornis and show that the only unambiguously identified specimen of the species—the holotype—is currently poorly diagnosed from Klallamornis abyssa Mayr and Goedert, 2016, which is from coeval strata of the Pysht Formation. Although the holotype of K. abyssa is larger than that of K. buchanani, there remains a possibility that plotopterids were sexually dimorphic in size. We describe the first ungual phalanx of a plotopterid, which is referred to K. buchanani, and report previously unknown elements of the large ?K. clarki and the first records of this species from the Lincoln Creek Formation. Current data indicate that plotopterids originated in the middle or late Eocene on islands off western North America, and we hypothesize that the radiation of these birds in the North Pacific Basin may have been related to the evolution of kelp forests.

Sedimentary Record of Paleogene Sequences in the Penyu and Malay Basins, Offshore Peninsular Malaysia

The Eocene to Lower Oligocene deposits of the Penyu and Malay basins are formed by fluvial-lacustrine deposits with marine influence in the latter. The sequence consists mainly of siltstone, with several intercalations of fine-grained sand and volcanic tuff. Based on well data, Mid-Upper Eocene sediments exist in Penyu Basin in the deeper parts of the half grabens and sub-basins. Hence, this implies the age of basin initiation at Mid-Eocene, rather than Oligocene as traditionally and commonly stated in the literature. By correlation, and as seismic evidences show, Eocene sediments also appear to exist in the deeper, undrilled parts of the Malay Basin, again implying that at the latest, a Mid-Eocene age of basin initiation.In the Penyu Basin, aprominent near-Base Oligocene Unconformity can potentially be correlated to the Base-Tertiary Unconformity in the adjacent Malay Basin, however the latter term implies all Tertiary sequences, including potential Paleogene deposits above the unconformity. Besides, we also observe intra-Eocene unconformities, called the Top N and Top O. The presence of Eocene strata is likely associated with an early phase of extensional tectonism, and probably related to the onset of rifting of the South China Sea continental crust.

Paleogene extension in the Northern Aegean: Colluvial/debris flow deposits of the Early-Middle Eocene in NW Thrace Basin, Turkey

The Thrace Basin consists of Paleogene–Neogene deposits that lie in the lowland south of the Strandja highlands in NW Turkey, where metagranitic and metasedimentary rocks occur. The Akalan Formation consisting of colluvial fan/debris flow deposits represents the base of the sequence in the northern Thrace basin where it is bounded by a right lateral strike-slip oblique fault called “The Western Strandja Fault Zone”. This formation exhibits a coarse-grained, angular and grain-supported character close to the fault zone which has releasing-bends. Fine-grained, rounded, and matrix-supported sediments occur away from the contact. During this study, the Akalan Formation is described for the first time as having larger benthic foraminifera (LBF) of Coskinolina sp of Ypresian–Lutetian, Nummulites obesus of early Lutetian, Dictyoconus egyptiensis of Lutetian, Orbitolites sp. of Ypresian–Bartonian, Miliola sp of early–middle Eocene, Idalina grelaudae of early Lutetian–Priabonian, Ammobaculites agglutinans, Amphimorphina crassa, Dentalina sp., Nodosaria sp., Operculina sp., Lenticulina sp., Quinqueloculina sp. and Amphistegina sp. of Eocene. This unit passes upward with a conformity into reefal limestones of the middle/late Eocene–early Oligocene Soğucak Formation. At times, the limestone overlies the conformity, there is an indication of a prograding sedimentary sequence. The new stratigraphic, paleontological, sedimentological and structural findings related to the NW Thrace Basin suggest a strong transtensional/extensional tectonic control for the initial Paleogene sedimentary deposition during the Ypresian–Lutetian period as shown by fossil content of the Akalan Formation. Right lateral-slip extensional tectonics appears to have had activity during the middle–late Eocene transgressive deposition of the Soğucak Formation when the basin became deepened and enlarged.

Detrital zircon U–Pb ages and Hf-isotopes from Eocene intermontane basin deposits of the southern Canadian Cordillera

Lower Eocene strata exposed in the hinterland of the southern Canadian Cordillera were deposited in extensional–transtensional basins and provide insights into the evolution of the orogen. We measured stratigraphic sections and collected 22 sandstone samples for detrital zircon uranium–lead (U–Pb) geochronology (n = 2995) and hafnium isotope (εHf) values (n = 67) in order to reconstruct the Eocene physiography and sedimentary history of the region. Early Eocene sedimentation in the interior of the southern Canadian Cordillera occurred in alluvial fan, fluvial, lacustrine and paludal settings in multiple compartmentalized basins. In most locations, detrital zircons have ages of ca. 50 Ma, which are interpreted to be derived from the syndepositional Challis–Kamloops volcanics. Several locations have dominant detrital zircon populations with ages between ca. 145 and 200 Ma, suggesting distinct sediment sources and paleodrainages within the southern Canadian Cordillera. Maximum depositional ages record coeval sedimentation across the southern Canadian Cordillera hinterland, supporting the hypothesis that upper crustal deformation and basin subsidence occurred at the same time across the orogen interior. εHf(t) values of ca. 50 Ma and 145–200 Ma detrital zircons vary between −16 and +12, with more evolved εHf(t) values in the eastern portion of the study area and more juvenile εHf(t) values in the west. Differences in εHf(t) are interpreted to reflect crustal changes across the region, likely related to underlying Laurentian basement rock. Detrital zircons from intermontane basins may provide an additional tool for examining crustal heterogeneity in cordilleran orogens.

New assemblage of cingulates from the Quebrada de Los Colorados Formation (middle Eocene) at Los Cardones National Park (Salta Province, Argentina) and the Casamayoran SALMA problem at Northwestern Argentina

In the Eocene deposits of Northwestern Argentina, the order Cingulata was recognized in the sedimentary levels of the upper and lower sections of the Lumbrera (Salta Province), Geste (Catamarca and Salta provinces), Quebrada de Los Colorados (Salta Province), and Casa Grande (Jujuy Province) formations. The traditional biochronological scheme associated the Geste Formation to the Mustersan SALMA (37.3–35.4 Ma; Priabonian), the lower section of the Lumbrera Formation to the Vacan Subage (44–46 Ma; Lutetian) of the Casamayoran SALMA, and the fossiliferous levels of the remaining units to the Barrancan Subage (39–42 Ma; Bartonian) of the Casamayoran SALMA. Nevertheless, recent dating obtained for the top of the lower section of the Lumbrera Formation supports a new geochronological framework for Northwestern Argentina, which changes the temporal assignation of the taxa that have been collected in this section, going from the Vacan Subage to the Itaboraian SALMA, affecting also the biochronology of the Quebrada de Los Colorados and the upper section of the Lumbrera formations, which are now constrained between 46 and 40 Ma (Lutetian). In this contribution, we present a new cingulate assemblage based on osteoderms collected in the basal levels of the Quebrada de Los Colorados Formation at Los Cardones National Park, Calchaquí Valley (Salta, Northwestern Argentina), which is constituted by a new taxon plus Pucatherium parvum and Parutaetus punaensis. In addition, we discuss all the Eocene cingulate associations reported for Northwestern Argentina taking into consideration the new geochronological framework.

(Bio)stratigraphic overview and paleoclimatic-paleoceanographic implications of the middle-upper Eocene deposits from the Ica River Valley (East Pisco Basin, Peru)

The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive.This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic-bioclastic sand-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8–41.2 Ma) through the Bartonian (41.2–37.7 Ma) to the early Priabonian (37.7–33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sandstone, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere.Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147–170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.

The Eocene−Oligocene transition in Nanggulan, Java: lithostratigraphy, biostratigraphy and foraminiferal stable isotopes

The Nanggulan section in south central Java comprises open marine sediments and volcanic deposits of Eocene–Oligocene age that accumulated in a marginal basin within the young Sunda Arc complex. A new borehole captures the stratigraphy and showcases the exceptional preservation of calcareous microfossils across an apparently complete Eocene–Oligocene Transition (EOT), a time interval significant for the initiation of continental-scale glaciation on Antarctica. Low-resolution benthic and planktonic foraminifera oxygen and carbon stable isotopes ( δ 18 O and δ 13 C) record increasing δ 18 O and δ 13 C in the basal Oligocene, allowing correlation to global records. Isotopic values imply warm temperatures and relatively high nutrients along the SE Java margin. The Nanggulan EOT is a valuable archive for reconstructing ocean–climate behaviour and plankton evolution and extinction in the Indo-Pacific Warm Pool. The borehole also adds to understanding of the early stages of Sunda Arc volcanism. Supplementary material: Supplementary figures, tables and appendices are available at https://doi.org/10.6084/m9.figshare.c.5429453

New genera of melikertine bees with facial modifications in Baltic amber (Hymenoptera: Apidae)

The tribe Melikertini (Apinae: Corbiculata) is an extinct group of highly eusocial bees presently known only from early to late Eocene deposits of Eurasia. Among melikertine diversity are a suite of species peculiar for their rather dramatic morphological specializations, at least in relation to modern corbiculate Apinae. Here we document two new species of Melikertini and utilize standard X-ray as well as propagation phase contrast synchrotron computed microtomography to further explore these and previously known species, revealing finer details not previously observable from melikertines. Accordingly, some species placed in the genera Melikertes Engel and Succinapis Engel are reëvaluated. Three new genera are characterized, as well as some further facial modifications not previously known for the tribe. New taxa and taxonomic changes presented are: Aethemelikertes emunctorii Engel, new genus and species; Haidomelikertes uraeus Engel, new genus and species; H. proboscidea (Engel), new combination; Amelikertotes Engel, new genus; Amelikertotes clypeata (Engel), new combination. Additionally, new records and taxonomic notes on other Baltic amber and Eocene bees are appended, with the following nomenclatural changes established: Palaeomacropis Michez & Nel is recognized as a megachiline rather than a melittid, and is transferred to Megachilinae where it is a new junior synonym of Ctenoplectrella Cockerell (new synonymy); Ctenoplectrella eocenica (Michez & Nel), new combination; a key is provided to species of Ctenoplectrella; Thaumastobombina Engel, new subtribe in Electrapini; Thnetobombus Engel, new subgenus in Protobombus Cockerell; Mesomelissa Engel, new subgenus in Electrapis Cockerell; Electrapis (Euglossopteryx) biesmeijeri (De Meulemeester et al.), new combination. A list of Eocene bees is appended.

New records of legless squamates from the lowest upper Eocene deposits of the Fayum Depression, Egypt

ABSTRACT The Eocene was a key interval for the diversification of squamates worldwide. However, little is known about their early evolution in Africa due to the scarcity of Paleogene fossil squamates from that continent. One of the most important Eocene vertebrate assemblages in Africa is known from the Fayum Depression of Egypt, but only a few lizards and snakes have been reported from these deposits. Here we report the first Paleogene record of the clade Amphisbaenia in Egypt, from the lowest upper Eocene Birket Qarun Locality 2 (BQ-2). It corresponds to a mid-trunk vertebra characterized by a depressed centrum with a flattened base, hemispherical synapophyses, and absence of a neural spine. Additional material from BQ-2 includes seven vertebrae attributed to colubroidean snakes. One trunk vertebra resembles those of early Eocene Procerophis from India while the remaining colubroidean vertebrae are referred to Renenutet enmerwer. Caudal vertebrae of Renenutet are described here for the first time. Similarities in the caudal vertebral morphology between BQ-2 Renenutet and Thaumastophis missiaeni from the lower Eocene of India reinforce the hypothesis of a close affinity between them. The presence of cf. Procerophis and Renenutet in Egypt adds to the evidence for terrestrial faunal exchange between Asia and northern Africa during the early/middle Eocene along the southern margin of the Tethyan Sea.

Geological structure and paleogeographic zoning of the Khadum formation in Pre‑Caucasus

Unconventional oil and gas resource development and exploration is the one of the most prospective concept in petroleum geology. High carbon Khadum facies are investigated as unconventional resources in the Precaucas basin and contain gas, gas condensate and oil accumulations. Oligocene and Lower Miocene structure, prospectivity and fields distribution are the one of the most relevant subjects nowadays. This study is focused on the main stages Late Eocene and Early Oligocene deposits formation and the paleogeography of the Khadum formation in the Precaucas oil and gas basin. The new prospective zones are developed in Khadum formation based on the complex analysis of seismic, paleogeography and lithofacies analysis.

Formica species (Hymenoptera, Formicidae, Formicinae) in late Eocene Rovno amber

A new species, Formica ribbeckei Radchenko & Perkovsky, sp. nov., is described based on four workers from late Eocene Rovno amber (Ukraine). It most resembles F. flori Mayr, 1868 but differs from the latter mainly by the 5-segmented maxillary palps with the preapical segment subequal in length to the apical one, and by the shorter first funicular segment. Fossil F. luteola Presl, 1822, F. trigona Presl, 1822, F. macrognatha Presl, 1822 and F. quadrata Holl, 1829 are considered incertae sedis in Formicidae. Thus, ten valid Formica Linnaeus, 1758 species (including F. ribbeckei) are known now from late Eocene European ambers. The diversity of Formica in the early and middle Eocene deposits of Eurasia and North America is considered. It is assumed that the genus Formica most likely arose in the early Eocene.

Role of the Early Miocene Jinhe-Qinghe Thrust Belt in the building of the Southeastern Tibetan Plateau topography

Understanding the role of southeastern Tibetan thrust faults in the development of plateau topography is key to our assessment of the geodynamic processes shaping continental topography. Detailed structural analysis along the ~400 km long Jinhe-Qinghe thrust belt (JQTB) indicates post Late Eocene thrust motion with a minor left-lateral component, inducing ~0.6 to 3.6 km of apparent vertical offset across the fault. The exhumation history of the Baishagou granite, based on thermal modeling of new apatite (UTh)/He and fission-track results, suggests an accelerated exhumation rate (~0.4 km/Myr) between 20 and 16 Ma, corresponding to ~1.7–2.4 km of exhumation. We interpret this fast exhumation as a manifestation of the activation of the Nibi thrust, a northern branch of the JQTB, resulting in the creation of significant relief across the JQTB in the Early Miocene. When compared with previous studies, our findings show that Cenozoic exhumation and relief creation in southeastern Tibet cannot be explained by a single mechanism. Rather, at least three stages of relief creation should be invoked. The first phase is Eocene NE-SW compression partly coeval with Eocene sedimentation. During the Late Oligocene to Early Miocene and coeval with the extrusion of Indochina, the second thrusting phase occurred along the Yulong and Longmenshan thrust belts, and then migrated to the JQTB at 20–16 Ma. The third phase involved the activation of the Xianshuihe fault and the re-activation of the Longmenshan thrust belt and the Muli thrust. Uplift in the hanging wall of thrust belts appears to explain most of the present-day relief in the southeastern Tibetan Plateau.